Reporter

It's HERE AND NOW. The world's most ambitious attempt to harness fusion as a source of nuclear power is taking shape in the south of France. Fusion is the process that drives the sun - atoms are forced together to release energy. And repeating it here on Earth could, in theory, offer an almost endless supply of electricity. The BBC's David Shukman reports.

(SOUNDBITE OF MACHINERY)

DAVID SHUKMAN: I'm in Provence in a great chiasm carved out of the rock. A sea of day-glow jackets marks this out as one of the largest construction sites in the world. This is Iter, an international project to build a new kind of nuclear reactor, powered by fusion. Fusion has long been promised as the great hope for cheap, abundant energy in the future. Well, this will show if it can work. And the man in charge of putting it all together is Ken Blackler. Fusion has always been a dream since the 1950s. Is it getting any closer?

KEN BLACKLER: It is. I mean as you can - as around us, we're in a construction site. So really, the construction of Iter has started. The manufacturing of the pieces have started around the world. So the train of Iter is now moving, and we're really working towards building Iter and then getting it operating.

SHUKMAN: The joke since the '50s is that fusion energy is always 30 years away and always remains 30 years away. Realistically, when might we get commercial fusion power?

BLACKLER: Well, in a sense we're now finished with the science. Iter will demonstrate the technology of fusion, which means we can then go and build a demo reactor. And we can look at the energy around about 2040, so it's decades, but it's - we can see the future now.

SHUKMAN: Now, we're looking around us at a great army of construction workers, cranes towering overhead. It's become a massive engineering project, this, but there must still be uncertainties about whether this can actually work as a viable commercial source of power.

BLACKLER: Yeah. At this point we've overcome the scientific challenges. We're quite certain about the science. And most of the technical or the technical challenges of the machine have also, we think, been solved now. So after that, for a commercial reactor, we have to worry about the cost. So that is an issue for the next - for the demo machine, to build the machine within a cost which can be commercially attractive, absolutely.

SHUKMAN: Given that fusion power is decades away, how do you personally remain motivated day after day when it's perfectly possible that this thing may never really work or that if there is electricity from fusion, it will be way down towards the backend of this century?

BLACKLER: Well, I think many of us come to the project because of the end point, because we think the project will contribute towards this energy source. But once you are here, the challenges of working with such an international project with day-to-day exchanges, with the interest of the technical challenges you have to deal, that keeps you going. That keeps you very interested. Every day there's challenges which are interesting.

SHUKMAN: The doubling of the costs and the doubling of the time taken to get this far, that doesn't put you off?

BLACKLER: No. I think that was - that's a sort of consequence of the move from science into the real world, into engineering. And now I think we've passed that phase, and now we're into the construction. And now, it's, you know, we're on the level field.